import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.List;
import java.util.Queue;

public class Niudaily{
   
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        List<Integer>[]grid=new ArrayList[n+1];
        for (int i = 0; i < grid.length; i++) {
            grid[i]=new ArrayList<>();
        }
        int m=sc.nextInt();
        boolean[]vis=new boolean[n+1];
        int[]dist=new int[n+1];

        for (int i = 0; i < m; i++) {
            int from=sc.nextInt();
            int to=sc.nextInt();
            grid[from].add(to);
            grid[to].add(from);
        }
        vis[1]=true;
        Queue<int[]>que=new ArrayDeque<>();
        que.add(new int[]{1,0});
        while (!que.isEmpty()) {
            int[]cur=que.poll();
            int from=cur[0];
            int d=cur[1];
            for (int next : grid[from]) {
                if(!vis[next]){
                    int newd=d+1;
                    vis[next]=true;
                    dist[next]=newd;
                    que.add(new int[]{next,newd});
                }
            }
        }
        System.out.println(dist[n]==0?-1:dist[n]);
        sc.close();
    }  
 
}